LS4 FAQs

LS4 Frequently Asked Questions (FAQs)

Folks often drop me questions via email (which I love) about LS4s and their W-Bodies. While I'm not a mechanic (I work in IT), I do my best to research what I can and share what I learn with my fellow enthusiasts. So, here are some questions that people frequently ask me. You should do your own research and speak to a mechanic before doing anything at all. Again, I'm not responsible for anything that happens to you or your ride.

What is an LS4? Do they still make LS4s?

An LS4 is a Fourth Generation LS-Series V8 made by General Motors (GM) that is mounted transversely (e.g. sideways rather than front to back / longitudinally) for Front Wheel Drive (FWD) application in the following W-Body vehicles:

2006 - 2009 Chevrolet Impala SS

2006 - 2007 Chevrolet Monte Carlo SS

2005 - 2008 Pontiac Grand Prix GXP

2009 Buick Lacrosse Super

LS4 engines displace 325 cubic inches / 5.3 liters; this displacement is arrived at with 8 cylinders set at 90 degrees in an aluminum block; the bore of the cylinders are 3.78" in diameter and the stroke is 3.62". LS4s have a 10:1 compression ratio.

In stock form, LS4s are rated at 303 horsepower and 325 ft-lbs of torque at the crankshaft.

LS4s are most similar to LS2s as they are both Gen IV LS-Series V8s that use the same '243 cylinder heads, but have a 13mm shorter crankshaft (10mm on the accessory / serpentine belt side and 3mm on the flywheel side).

LS4s are no longer being installed in new GM vehicles; the last of the factory-installed LS4s were produced for the 2009 model year.

What kinds of gasoline can an LS4 use?

LS4s are designed to run on on 91+ octane gasoline. They should not run on 87 or 89 octane and should never, ever be used with diesel gasoline.

My LS4 is burning oil! What do I do?!

There are a number of reasons why this can happen. Some of them are easy to resolve, others involve rebuilding the engine. One common reason that a lot of folks have reported to me and through the various forums and web sites that I'm on is because of the Displacement on Demand (DoD) / Active Fuel Management (AFM) system, especially in earlier implementations. Some report being low a quart of oil for every thousand miles they drive. Given that our LS4s hold 6 quarts (5.7 liters) of oil, losing 5 quarts in 5,000 miles leaves the engine almost dry.

One thing to try is to disable the DoD / AFM system. Many of those who have reported oil consumption issues have subsequently reported that disabling DoD / AFM solved their problem immediately.

How do I disable Displacement on Demand (DoD) / Active Fuel Management (AFM)?

There are two common ways to disable DoD / AFM -- hardware and software. The hardware solution is more involved and more permanent than the software solution.

Option 1 -- software solution

Use a tuner. This takes seconds and can be as easy as -- literally -- selecting a "Non-DoD Tune" from a DiabloSport tuner (including the Predator, the inTune, and the Trinity). It requires zero mechanical knowledge and can be re-enabled in a heartbeat. The only cost is the tuner; you can buy a DiabloSport Predator for around $300 online, so this isn't too expensive. Alternatively, you can also take your LS4 to a performance tuning shop and ask them to disable it for you as well, but that's likely even more expensive than using a DiabloSport tuner.

Option 2 -- hardware solution:

Tap and plug the DoD towers in the block so that oil pressure will not engage the DoD system's special lifters. In fact, while you're in there, you can also replace the stock LS4 valley cover / VLOM, the DoD lifters, and even swap in a non-DoD camshaft that's tuned to your specific application. This is the least expensive solution (the plugs cost less than $10 for 8 plugs), but it also involves the most mechanical knowledge. In order to access the DoD towers, you'll need to remove the intake manifold and that will necessitate a pair of new intake manifold / cylinder head gaskets. Even with this gaskets, this is much less expensive than using a tuner.

During certain driving conditions, the ECM / PCM may opt to deactivate four cylinders and only run on 4 cylinders. This helps promote improved fuel efficiency when cruising while providing additional power during acceleration.

When activated, DoD forces pressurized oil through DoD towers cast into the block. The oil pressure causes the intake and exhaust valve lifters to collapse; valve spring pressure holds the intake and exhaust valves closed. Fuel is no longer injected into the (now) deactivated cylinders. Similarly, the ignition system for the deactivated cylinders is stopped so that the spark plugs in the deactivated cylinders no longer fire.

What intake manifold options are available for LS4s?

Well, there aren't a whole lot of options, so let me manage your expectations right from the start. Our intake manifolds are on "backwards," our alternators (and their brackets) are right in the way, and our '243 heads have "cathedral" style ports.

So, the easiest intake manifolds to start with are those from other engines that use cathedral style ports, including LS1s, LS6s, and LS2s. Of those options, LS1s are the cheapest and easiest to find, the LS2s accept larger throttle bodies, and the LS6s flow the air for stock LS4 heads / blocks.

LS1 / LS6 intake manifold swaps are the most common; a swap with one of these will have a noticeable impact on torque and high-RPM breathing. That said, there will still be some modification and fabrication involved. You'll also need to get creative about your throttle body if you have Doug Thorley headers as the new crossover pipe tends to be right in the way.

Intake manifolds from other LS-series engines are much more complicated to deal with, mainly because the later (post LS2) engines have heads that use rectangular ports. You could swap cylinder heads to facilitate matching a later intake manifold, but those later heads also require larger bores (often 4.00"+) than our LS4s provide (3.78"). You could resleeve the block (and all that entails) to match higher-flow cylinder heads, but now you're looking at a project that costs more than the vehicle is worth just to go with a different intake manifold.. So, I'll have to say that it's technically possible, but realistically it just doesn't make sense.

There are a variety of aftermarket intake manifolds on the market, not to mention custom (e.g. sheet metal) intake manifolds. Most will likely not fit because of the alternator's location. Even if that doesn't get you, hood clearance probably will.

Which cylinders are which? Which cylinders are deactivated by DoD? What is the firing order?

What happened to the Hogan Performance downpipes?

The owner (Curt Hogan) made a business decision to step away from the fabrication of Hogan Performance downpipes for personal reasons. As a result, they're no longer offering bolt-on downpipes.

It's possible to custom fabricate a new downpipe, particularly if you (or your exhaust shop) has access to a mandrel bender.

What is a "Resonator Delete?" Why would I want to remove the resonator?

Well, the resonator is a device that's meant to quiet the exhaust tone, especially inside the cabin when the vehicle is running in 4 cylinder mode. It's basically another muffler.

If you remove the resonator and replace it with straight pipe, the exhaust tone will be a little bit louder and with more of a rasp than before. Also, exhaust gasses will leave the vehicle more smoothly and efficiently, leading to a decrease in backpressure.

However, if you leave DoD / AFM active, when the engine drops into 4 cylinder mode, the exhaust sound will be much louder inside the cabin -- it sounds like you have an annoying helicopter in your back seat.

What about the Catalytic Converter? Can I remove that?

Well, yes and no. If you want to drive your car on public highways and you want to pass your state's inspection laws, you'll need to retain your catalytic converter. If you remove your catalytic converter, you'll be choosing to release some pretty noxious chemicals into the atmosphere. The planet will hate you. At the same time, you'll get a tiny power gain (maybe 1 - 2 ft-lbs) and the exhaust note will be even more aggressive.

However, catalytic converters have advanced to the point where they're very efficient and create very little backpressure in the exhaust system. Any gains you may see from removing it will be microscopic, at best.

What is an exhaust cutout? Why would I want one? Where would I put it?

An exhaust cutout is a device placed in the exhaust system that, when open, allows exhaust gasses to go along one route instead of the default route. So, the most common use of a cutout is to allow exhaust gas to bypass the car's mufflers and vent directly to the outside world. When our LS4s run with cutouts open, it's like they have no mufflers. The sound is very loud and very aggressive. Some liken the sound to that of a pickup truck.

While your neighbors will come to know the inner glory that is the deep rumble of an LS-series V8 engine, they will quickly come to hate you and your car. The police won't like the sound either. Running an open cutout is about as legal as running without a catalytic converter, except you're telling everyone around you that you've done something to your car that they may find to be obnoxious, annoying, and very rude.

There are several innovations that have made cutouts more interesting than a Y in the exhaust pipe. For example, some people make "electric cutouts" that come with a butterfly valve that goes on the end of the cutout. When actuated (generally by a toggle in the cabin), they can open and close the cutout in a matter of seconds.

Not content with a cabin-mounted switch, there are some manufacturers that have included a remote control (e.g. key fob) device that allows you to open and close the cutout remotely. That said, most cutout manufacturers strongly recommend that an electric cutout only be operated when the engine is turned off or running at idle; otherwise, the pressure from the exhaust system may damage the electric cutout's motor.

If you do decide to go with an exhaust cutout (for off-road use only), then there are a number of locations that you can consider. The placement that I went with is on the Y pipe after the resonator and right before the mufflers, on the passenger side of the car. This puts the cutout right in front of the passenger rear tire.

Another location some folks have tried is the downpipe. There are a few obstacles with this location. First, it's in front of the catalytic converter and the O2 sensors. As a result, after a little while with the cutout open, the CEL will come on and a code will be thrown saying that the catalytic converter isn't working properly. Even if you have this code ignored (e.g., via a custom DiabLew tune), then you'll still have problems when you get your car inspected for emissions. Also, the cabin noise would be quite loud and the smell would be awful, especially if you're just idling and not rolling. Lastly, it'll be a tight fit for components that can get really, really hot, so you risk damaging nearby components.

Yet another option to replace the resonator with straight pipe and put the cutout onto the straight pipe. You'll run into the same problems as before, especially with fitment and proximity to other components.

I have an electric cutout with a remote control made by DMH Performance. It works great, they love it at car shows, and it comes with a 4 year warranty.

The installation instructions for the Doug Thorley exhaust headers (THY-340-C) don't give me torque values. What do I tighten the bolts to?

The instructions (link) don't mention the torque specifications for the bolts that attach the headers to the block or the bolts that attach the headpipe to the catalytic converter; they say to tighten to "factory torque specifications." So, for your convenience, here they are out of the Haynes repair manual:

Exhaust manifold bolts

Step 1: 132 inch-pounds

Step 2: 15 foot-pounds

Exhaust pipe flange nuts: 18 foot-pounds

Exhaust manifold heat shield bolt: 80 inch-pounds

You won't need the heat shield bolts, but I'm including them for folks who are searching for specifications for the stock iron exhaust manifolds.

Also, please remember that the LS4's block is all aluminum, so please don't over-tighten these bolts; it's hard enough to get at them to tighten the bolts down as it is. Having to repair the threads with the engine in the car would be a nightmare.

How do I get the battery out?!

I know... I know... it's a nightmare. It's really cramped in there due partly because you have a big V8 engine stuffed under the hood!

Well, you'll need to remove the passenger side structural brace first. Then, you'll need to move the fuse housing up and out of the way. Lastly, there are two bolts on the bottom of the battery pan that are used to hold the battery in place. You'll want to use a socket on an extension in order to access these two bolts. You'll also want to use a U-joint to give yourself a little better angle to work with. I've also found that having somebody there to help hold stuff out of the way when you go to remove / (re-)install really helps.

When you go to acquire a replacement battery, I've found that the Optima batteries are slightly smaller, slightly lighter, and their sides are rounded, so they're actually much easier to remove than the stock batteries.

It's hard to launch these vehicles from stop -- I get excessive wheel spin!

Yeah, that's the downside of a heavy (3,700 lbs) Front Wheel Drive vehicle with a high-torque V8. When we accelerate, weight is transferred off of the front (drive) wheels. You'll have to be light on the accelerator when going from a dig; otherwise, you'll spin the wheels and chew up your tires.

I get excessive torque steer when launching!

Yeah, no, what you're experiencing is is the Traction Control System trying to help you retain control of the vehicle despite the fact that the tires are spinning at different rates.

When I get into a turn and I mash on the gas, the engine cuts out for a second.

Yeah, don't do that. The car has determined that the end of the world (as far as it's concerned) is nigh and in an attempt to help you retain control of the vehicle, it has cut engine output. There isn't an easy way to disable this, so go a little lighter on the gas in the corners.

I want to lower my car. Can I do that? What coil springs do you recommend?

Well, I totally intend to lower my car at some point. Since I haven't done it yet and I don't have any direct, personal experience with any of the aftermarket products on the market, I don't feel comfortable in making any recommendations yet.

Also, a lot depends on your taste, your driving style, your roads and curb cuts, and how you execute your suspension project. For example, someone may love ABC springs while the next person may find that they're way too stiff and they like XYZ springs instead.

Moreover, you have to look at the overall suspension as a complex, integrated system. Changing one piece -- like the springs -- often has a direct effect on other components. For example, if you lower the car by modifying / swapping the coil springs, the struts will no longer operate within the design parameters set by the engineers; as a result, lowering the car often requires that you swap the shocks and struts out with components that are designed to work within the new ride parameters.

Also, let me caution you further and point out that the suspension is a key component of your ability to drive your vehicle safely. If the engine creates too much (or too little power), chances are you won't accelerate the way you anticipate; if the suspension is not setup properly for the conditions and environment, you could easily lose control of the vehicle and face dire consequences.

How did you make your wheels black? They really tie the look together!

I used PlastiDip. It's like a rubberized spray paint. Not only does it affect the appearance (e.g. the wheels are painted black), but it also keeps a lot of the nasty from the outside world off of the wheels. PlastiDip can also be removed easily (as compared to traditional spray paint).

When I use PlastiDip on my wheels, they look dry, dirty, and flat. I hate it!

Well, I've found that spraying some wet tire shine on the dry PlastiDip really deepens the color and gives the finish a nice shine. I wind up re-spraying them every few months but it only takes seconds. Also, when applying the PlastiDip, take care to use good spray painting technique -- make sure the wheel is as clean as possible and use several quick, light, even coats.

If you still really hate it, peel it off. Just be careful not to scratch the polish on the wheels.

Where did you get those fluid reservoir covers?!

They were originally fabricated by MRZ Performance. I don't have a link to them because I can't seem to find them on their redesigned site.

I want to get into modifying my LS4. What upgrades would you recommend?

The first thing I would do is to acquire a tuner for my ECM / PCM. I would almost certainly buy another DiabloSport tuner. Once I got the tuner, the very first thing I would do would be to disable the Displacement on Demand (DoD) / Active Fuel Management (AFM). This would immediately give you more power in a way that is instantly reversible (e.g. you can restore the stock tune) and doesn't require you to get your hands dirty at all.

After a tune, I would look at Strut Tower Braces (STBs). They add a few pounds to the vehicle, but they dramatically reduce chassis flex and help you keep the wheels planted to the ground throughout curves. You'll be able to take turns quite a bit faster and you'll be able to get on the power more quickly than a similar LS4 without STBs. If you wanted to get just one, I would look at the rear STB as the firewall and the engine bracing does a pretty good job of reducing chassis flex in the front of the car.

The next thing to look at are the tires. I would recommend that you study your driving habits, the weather and climate patterns where the car will be driven, and the rules on what types of tires are allowed where you'll be driving the car. If you're living at the north pole, drag slicks will be about the worse thing you could get for your car. If you plan to participate in any form of motorsport, your group or car club may have rules about DOT-spec tires that may affect your car's classification. If you commute two hours a day on the open highway and you never go to the track, a super-soft tire may not be in your best interests and a harder, longer-wearing tire might be a better match.

After that, I would look at the air intake system. For example, is your air filtering element clean? Could it be replaced with a higher-flowing, cleanable element (like the K&N filters)? For even better performance, the stock air box can be replaced with a Cold Air Intake system, like those made by K&N, AEM, CAI, etc.

Then, I would look at changing the spark plugs. The stock spark plugs -- in some applications -- require increased knock retard. NGK's iridium plugs tend to stave off knock better than traditional stock spark plugs. That said, changing the rear four spark plugs can be a bit of a chore as most of the work is done blindly and at odd angles.

Next, I would look at replacing the stock downpipe with a unit with a mandrel bent aftermarket unit. Replacing the stock downpipe helps flow exhaust gasses more smoothly and with less backpressure.

Then, I would look at a custom tune. If you're using a DiabloSport tuner, a DiabLew Tune by DiabLew / 06MonteSS would give your car even more power over stock or even DiabloSport canned tunes. His tuning procedure involves using your DiabloSport tuner to gather engine log data, extracting that data to a computer, and emailing him the data. He works his magic and you get a custom tune for your specific car back by email. You then transfer the custom tune to your tuner and import it into your ECM / PCM.

This is pretty much all of the low-hanging fruit. After this, the work and / or expense involved tends to increase from $200 - $300 parts that you can install with simple hand tools to $700+ parts that require specialized tools (e.g. welding equipment) and / or training.

Examples of these more involved projects include a catback exhaust (e.g. everything behind the catalytic converter, such as the resonator, the Y pipe, the mufflers, and the exhaust tips), exhaust headers, replacing the intake manifold, removing weight from the vehicle (e.g. removing rear seats, the sound system, air conditioning, power steering, etc.), swapping the transmission for a "built" unit (Triple Edge Performance (TEP) provides an excellent upgrade) and various suspension upgrades.

After that, the last thing to look at is the engine itself. Our LS4s are Gen IV LS-Series V8s and, as such, they share some common characteristics with other LS-Series V8s (e.g. 4.40" cylinder bore spacing). Unfortunately, our LS4s have a number of differences that are unique to our engines. For example, our crankshafts are shorter (13mm) than non-LS4 crankshafts, our accessory / serpentine belts are routed differently than other LS-series engines, our intake manifolds are "backwards" as compared to other engines, etc. Many of these differences are a result of the tradeoffs of transverse mounting a V8 in a FWD application.